SOUND, TYPES OF SOUND, INTERFERENCE OF SOUND, CALCULATION OF VELOCITY OF SOUND IN AIR, NEWTON'S FORMULA, LAPLACE'S FORMULA, DOPPLER EFFECT, ECHO, RESONANCE, MAGNETO STRICTION & PIEZO ELECTRIC PRODUCTION OF SOUND, APPLICATION OF SOUND

1. SOUND
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2. INTRODUCTION
 Sound waves are longitudinal waves that can
travels through any material medium with a
speed that depends on the properties of the
medium
 As sound travels through a medium, the
particles of the medium vibrant along the
direction of motion of the wave
 This is in contrast to a transverse wave where
the particles motion is perpendicular to the
direction of propagation
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4.  The displacement that occurs as a result of
sound waves involved the longitudinal
displacements of individual molecules from
their mean or equilibrium positions
 This results in a series of high and low pressure
regions called compression and rarefaction
respectively
 “Sound waves are longitudinal waves that travel
through all media in the form of compression
and rarefactions”
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6. ORIGIN OF SOUND
 Sound is
 A form of energy made by vibration
 When an object vibrates it causes the air
particles around it to move
 These particles bump into particles close to
them and this continues until they run out of
energy
 Sound is a variation in the pressure of the
air of a type which has an effect on our
ears and brain
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7. TYPES OF SOUND
 Sound waves are often categorised
into three group
 1. Audible – Hear easily
 2. Infrasonic – inaudible sound
 3. Ultrasound – inaudible sound
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9.  AUDIBLE AND INAUDIBLE WAVE:
 Produce compression and rarefactions in
air. However no audible sounds are
produced because the frequency of such
vibrations is too low (<20 hz) to affect our
auditory nerves.
 Likewise if the frequency of sound is high
(>20 khz), no sound is heard by the
human ear. It is because the vibrations
are so rapid that auditory nerves do not
respond to them
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10.  1) AUDIBLE WAVES:
 Audible waves are sound waves that
human ear can hear
 The range of human hearing is 20 HZ to 20
Khz. In other words, we cannot hear
waves of frequency below 20 hz or above
20 khz
 The audible waves can be generated in a
variety of ways such as by musical
instruments, human vocal cords and
loudspeakers 14-09-
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11.  2) INAUDIBLE WAVES:
 Those waves which human ear cannot hear are
called inaudible waves
 There are two types of inaudible waves like
infrasonic and ultrasonic
 Infrasonics are longitudinal waves with
frequencies below 20 hz. Earthquake waves are
an example
 Ultrasonic waves are longitudinal waves with
frequencies above 20 khz. For example they can
be generated by inducing vibrations in a quartz
crystal with an applied alternating electric field.
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12.  Sound may be broadly classified into two
general group:
1. Musical sound
2. Noise
 The difference between a musical sound
and noise is subjective, exa- its depends
upon the sense of a person
 A sound which is musical to someone may
be noise to others
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13.  Musical sound
 It is a pleasant, continuous and uniform sound
produced by regular and periodic vibration
 E.g- sound produced by tuning fork, flute, piano
etc
 In musical sound there is no sudden change in
loudness
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15.  Noise
 It is an unpleasant, discontinuous and non uniform
sound produced by irregular succession of
disturbances
 All sounds other than musical sounds are noise
 E.g- sound produced by a falling brick, clapping of
two wooden blocks etc
 In noise there is sudden changes in loudness
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16. CHARACTERISTICS OF SOUND
WAVES
 Sound waves are characterised by its
pitch (frequency), loudness (intensity)
and quality.
 The speed of the sound depends on the
medium transmitting it
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18.  1. AMPLITUDE- it is maximum displacement
of the medium from its equilibrium state
when a mechanical wave passes through
the medium. The amplitude of wave is
denoted by “a”.. SI is “m”
 2. WAVELENGTH- the distance between two
successive crest and two successive trough
is called wavelength of the wave. It is
denoted by “λ” .. SI is “m”
 3. FREQUENCY – The frequency of wave is
the number of complete cycle that pass a
given point in one second. It is denoted by
“f”. Unit of frequency is Hz. 14-09-
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20.  4. TIME PERIOD: the period of a wave is the
time taken by the wave source to complete
1 vibration or cycle. It is denoted by “T”..
SI is “sec”.. 1/F
 5. WAVE VELOCITY: The distance covered by
a wave in one second is called wave
velocity. It is denoted by “v” and is
measured in m/s in SI units
 6. VIBRATION: any regularly repeated to
and fro motion of change is known as
vibration
 7. PHASE : The stage in a cycle that a wave
has reached at a particular time from some
reference point.
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21. RELATION BETWEEN WAVE
VELOCITY, FREQUENCY &
WAVELENGTH
 The velocity of a wave is v, time period T,
frequency f and wavelength λ.
 By the definition of wavelength,
 Wavelength = Distance travelled by the wave in
one time period, i.e., in T second.
 Or wavelength = Wave velocity x Time period
 Or, λ = v x T
 Or, λ = v x 1/F [ T = 1/F]
 Therefore, v = Fλ
 Therefore, Wave velocity = Frequency x
wavelength
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22. INTERFERENCE OF SOUND
WAVES
 When two or more wave of sound of same
frequency travelling in almost same direction
superimpose, the resultant intensity in the region
of superimposition is different than the intensity
of individual waves.
 The modification in the distribution of intensity
of sound in the region of superposition is called
interference
 Depending upon the way the waves superimpose,
the interference is of two types:
 1) Constructive Interference
 2) Destructive interference
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24. CONSTRUCTIVE
INTERFERENCE
 When the waves superimpose in such a way that their
maxima and minima correspond with each other, the
resultant amplitude is the sum of the amplitudes due to
separate waves
 As the intensity is proportional to the square of the
amplitude and hence the resultant intensity at this
point is increased
 This phenomenon is called constructive interference
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25. EFFECTS
 In constructive interference, two waves
of sound reinforce each other
 In constructive interference, one can hear
a louder sound
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26. DESTRUCTIVE INTERFERENCE
 When the waves superimpose in such a
way that the maxima of one corresponds
with the minima of other, the resultant
amplitude is equal to the difference of
the amplitude due to separate waves.
This is termed as destructive interference
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27. EFFECTS
 In destructive interference, two waves
cancel the effects of each other
 Due to destructive interference we can
not hear sound or the intensity of sound is
decreased
 Thus, due to phenomenon of interference
we get maximum sound (due to
constructive interference) and minimum
sound (due to destructive interference)
which are called louder sound and null
sound respectively
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28. CALCULATION OF VELOCITY
OF SOUND IN AIR
 NEWTON’S FORMULA:
 NEWTON’S Assumed that the propagation of sound waves
in air is an isothermal phenomenon.
 i.e – a process in which temperature remains constant and
boyle’s law holds good (a relation concerning the
compression and expansion of a gas at constant
temperature)
 He argued that the small amount of heat which is
produced at compression is rapidly taken away to the
places of rarefaction where a slight cooling is produced
 In this way the temperature of the gas remains constant
 Thus for a given mass of gas at pressure P and volume V
 PV= CONSTANT 14-09-
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29.  According to theoretical consideration v = √E/ρ
 Where E = Coefficient elasticity of medium, ρ = density
of medium
 But in this we are taking air/gas as medium so
considering bulk modulation  v =√B/ρ
 According to newton's assumption this is isothermal
process  during compression and rarefaction
temperature is not changed  v = √Kiso /ρ ….. (1)
 During compression  pressure is increase
 During rarefraction  pressure is decrease
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30.  If PV = CONSTANT, By differentiating, we get
 P.dv + V.dP = 0  P.dv = - V.dP
 P = dP / - (dv/V) = change in pressure/ Volume strain =Kiso
 Substituting this value of P in the velocity expression
v = √Kiso /ρ = √P / ρ ….. (2)
 This is newton’s formula.
 V = √P / ρ = √76× 13.6 × 980 / 0.00129 = 280 m/s
 where P= h.d.g = (height = 76 cm of hg, density = 13.6 gm -3, gravity =
980 cm/s2 )
 Where ρ = 1.293 kg/m 3 = 0.00129 g/m3
 The experimental value of the velocity of sound in air at
N.T.P is 332 m/s
 Difference between the experimental and theoretical value
of velocity of sound in air = 332 – 280 = 52 m/s  16 %
difference between actual value
 So newton’s formula is not acceptable
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31. LAPLACE’S FORMULA
 Laplace pointed out that the propagation of sound
waves through air is an “ISOTHERMAL PROCESS”(As
suggested by newton’s formula) but it is an adiabatic
process
 He argued that due to the reasons
 1. that compression and rarefaction in sound waves take place
very rapidly
 2. large distances between compression and rarefactions
 3, poor conductivity of air, there is no appreciable heat flow from
regions of compressions (temp slightly high) to the regions of
rarefactions (temp slightly low)
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32.  Thus the conditions do not remain isothermal (i.e
temp changes)
 The relation between pressure and volume of air is
governed by the adiabatic relation,
 pVγ = Constant, where γ is the adiabatic constant….
(1)
 So according to laplace formula
 The value of “γ” for air is 1.41 (value of adiabatic
normal ratio) substituting the value of γ, P and ρ we
get
 V = √1.41 ×76× 13.6 × 980 / 0.00129 = 331.6 m/s
 So this value is good in agreement with the
experimental value
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33. DOPPLER EFFECT
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35. DEFINITION
 When a source generating wave moves relative to an
observer, or when an observer moves relative to a
source, there is an apparent shift in frequency
 This apparent change in frequency due to the motion of
the source (receiver) is called the Doppler effect, after
Christian Doppler (1808-1853), the Austrian physicist
who first explained this phenomenon
 The Doppler effect occurs for all types of waves
whenever there is a relative motion between the source
of waves and the observer
 The greater the speed of the source, the greater will be
the Doppler effect
 “the apparent change in the observed frequency of a
wave due to the relative motion between the source of
waves and observer is called Doppler effect”
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37. RESTING SOUND SOURCE
 The Doppler effect occurs when a source of waves moves
relative to the observer
 You have certain experiences this effect with sound. You are
familiar with the rise and subsequent drop in pitch of an
automobile horn as it approaches and then passes
 In other words, frequency of sound is raised when the source of
sound approaches you and lowered when the source is moving
away from you
 fs = fo (where fs is source of frequency & fo is observer
frequency)
 Person hearing sound  observer
 Emitting sound  source
 Acc to this 2 situations
 1. when the source moves  stationary observer
 2. when the observer moves  stationary source
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38.  The relationship describing the Doppler shift for
moving source is given by
 fo = v/v±vs × fs
 Where
fo = apparent frequency
v = velocity of sound
vs = velocity of source of sound S
fs = frequency emitted by the source
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40. SOUND SOURCE MOVING
TOWARDS STATIONARY OBSERVER
 Apparent frequency  fo = v/v-vs × fs
 since (v-vs) < v, fo > fs
 so the apparent frequency increase when
the source of sound moves towards the
stationary observer
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41. SOUND SOURCE MOVING AWAY
FROM OBSERVER
 Apparent frequency  fo = v/v+vs × fs
 since (v+vs) > v, fo < fs
 so the apparent frequency decrease when
the source of sound moves away from the
stationary observer
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42. SOURCE
NEAR
OBSERVER
SOURCE
AWAY FROM
OBSERVER
OBSERVER 
NEAR SOURCE
OBSERVER
AWAY FROM
SOURCE
fo = v/v-vs
× fs
fo = v/v+vs
× fs
fo = v+vo/v
× fs
fo = v-vo/v
× fs
(v-vs) < v,
fo > fs
(v+vs) > v,
fo < fs
(v+vo ) > v,
fo > fs
(v-vo ) < v,
fo < fs
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43. OBSERVER MOVE
 fo = v±vo / v × fs
 Where fs = frequency emitted by the source
fo = apparent frequency
v = velocity of sound in air
vo = velocity of observer O
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44. SOURCE STATIONARY AND
OBSERVER MOVING TOWARDS IT
 Apparent frequency  fo = v+vo / v × fs
 (v+vo ) > v , fo > fs
 When observer is moving towards a stationary
source of sound , the apparent frequency is
increased
 An observer moving towards a stationary
source hears an increase in frequency
because he intercepts the crests more
frequently than he would if he were
stationary 14-09-
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45. SOURCE STATIONARY AND
OBSERVER MOVING AWAY FROM IT
 Apparent frequency  fo = v-vo / v × fs
 (v-vo ) < v , fo < fs
 When observer is moving away from a
stationary source of sound , the apparent
frequency is decreased
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46. ECHO
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47. INTRODUCTION
 Echo are sound waves that are reflected back 
when the sound wave hits a flat, firm surface
 In audio signal processing & acoustics an echo
(plural echos) is a reflection of sound, arriving at
the listener some time after the direct sound
 Typical examples are the echo produced by the
bottom of a well, by a building or by the walls of
an enclosed room and an empty room
 A true echo is a single reflection of the sound
source
 It word echo derived from the greek word
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48.  An echo can be explained as a wave that
has been reflected by a discontinuity in
the propagation medium and returns with
sufficient magnitude
 Echoes are reflected off walls or hard
surfaces like mountains
 Echoes may be desirable (as in sonar) or
undesirable (as in tele-phone system)
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49. Application of ECHO
 1. To find out submarines from surface
 2. in fishing boats, to find out large shoals
of fish
 3. To measure the depth of the sea
 4. To locate a sunken shipwreck or cargo
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50. RESONANCE & VELOCITY OF
SOUND BY RESONANCE METHOD
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51.  RESONANCE – when a vibrating objects set up
air vibrations in an enclosed space, the sound
vibrations in the air very weak at some
frequencies and strong at other frequency
 The frequency at which the sound vibrations
are strong are called resonant frequency of the
system and the phenomenon is known as
resonance
 “The phenomenon of making a body vibrate
with its natural frequency under the influence
of another vibrating body with the same
frequency is called resonance” 14-09-
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52.  When 2 waves of equal wavelength and amplitude propagating
in opposite directions  superimpose on each other  then
interference occurs and the resultant wave is called a standing
wave
 In standing wave the particles of the medium at certain points
do not oscillate  called as nodes
 At certain point the particles of the medium have maximum
amplitude of oscillation  called as antinode
 In standing waves , the distance between
 Two consecutive nodes / antinodes  λ/2
 A node & successive antinodes  λ/4
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53. SINGLE LOOP PATTERN
 In fig , there is only one antinode which is at the centre
of the string and it is called single loop pattern
 Here L= λ/2
 λ = 2L
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54. TWO LOOP PATTERN
 This pattern has three nodes and two successive
antinodes and it is said to be a two loop pattern
 Here for the left and right going waves have must have
the wavelength λ = L
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55. THREE LOOPS PATTERN
 Third pattern is shown in fig
 It has four nodes and three antinodes  its called three
loops pattern
 Here the wavelength is λ = 2/3 × L
 So continues in this way wavelength is λ = 2/n × L
 Where n = 1,2,3,4….
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56. Resonance frequency
 The resonance frequencies that corresponds to these
wavelength are given by, f = v/λ
 Where λ = 2/n × L
 So f = nv / 2L (where n =1,2,3…..)
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57. ULTRASONIC
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58. INTRODUCTION
 The word ultrasonic combined the latin roots
ultra  beyond + sonic  sound
 Ultrasonic waves refers to sound waves
produced by an object vibrating at a frequency
higher than the human ear can hear (above 20
khz)
 By using modern techniques it has become
possible to produce ultrasonic waves of
frequency upto 25 billion Hz  has wavelength
of 10 -8 m, comparable with x ray wavelength
 An ultrasonic wave is highly energetic and has
extremely short wavelength becoz of its high
frequency & energy
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59.  The use of ultrasonics, especially in the
field of medicine & in various industries is
because of its small wavelength & high
energy
 The field of ultrasonics have applications
for imaging, detection and navigation
 Sound waves having frequency less than
the audible range (< 20 hz) are called
infrasonic
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60. PROPERTIES OF ULTRASONIC
WAVES
 1. They are likely energetic
 2. Just like ordinary sound waves, us waves get
reflected, refracted & absorbed
 3. Their speed of propagation depends upon their
frequency
 4. US show very negligible diffraction due to their
small wavelength . hence they can travel over long
distances without any loss of energy
 5. The liquid through which US wave pass, behaves as a
diffracting grating under monochromatic light
 6. They produce intense heating effect when passed
through a substance
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61. ULTRASONIC PRODUCTION
 US waves cannot be produced by the usual methods, like
from a diaphragm of loudspeaker fed to alternating
current
 This is due to the fact that at very high frequency the
inductive effect of loudspeaker coil is so large that
practically no current passes through it
 Moreover, the diaphragm of a loudspeaker cannot vibrate
at such high frequencies
 Therefore, different methods are specially used for the
production of US wave
 US Waves are produced by the 2 methods
 1. Magneto striction generator / oscillator  100 kHz
 2. Piezo electric generator/ oscillator  above 100 kHz
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62. MAGNETO-STRICTION
GENERATOR
 Based on the phenomenon of “magneto striction
effect”
 Principle- Magnetostriction effect
 When a ferromagnetic rod like iron / nickel is
placed in a magnetic field parallel to its length,
the rod experiences a small change in its length 
called magnetostriction effect
 The change in length (increase/decrease) produced
in the rod depends upon the magnitude of the
magnetic field, the materials and is independent
of the direction of the magnetic field applied
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64.  If the rod is placed inside a coil carrying an alternating
current , then it suffers the same change in length for
each half cycle of alternating current
 This result in setting up vibrations in the rod whose
frequency is twice that of alternating current
 Ordinarily the amplitude of the vibrations of rod is small
 the frequency of the alternating current is the same
as the natural frequency of the rod, then resonance
occurs and the amplitude of vibration is considerably
increased
 Sound waves are now emitted from the end of the rod
 Moreover if the applied frequency is of the US frequency,
the rod sends out US waves
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65. CONSTRUCTION
A B
NPN
Transister
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66.  A ferromagnetic rod AB made up of Ni is clamped in middle
 c as shown
 Coil of wires L , L1 are winded at the ends of A & B
 One end of the coil L1 is connected to the base of an NPN
transistor and the other end of coil L is connected to the
emitted and the negative terminal of a battery
 A variable capacitor C1 is connected across the coil L
 One end of the variable capacitor is connected to the
collector circuit, whereas the other end of the variable
capacitor is connected to the positive end of the battery
through a mA
 The natural frequency of the rod is given by n =
P/2L√E/D….. (1)
 Where L is the length of the rod, E is young’s modulation,
D is the density of the rod materials and P is the harmonic
modes 1,2,3…. etc 14-09-
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67. WORKING
 When battery is switched on, the circuit L C sets up
alternating current of frequency f = 1/2∏√LC in
collector circuit
 This alternating current flows through coil L1 , it causes
a corresponding change in the magnetisation of the rod,
which causes a change in the length of the Ni rod
 This change in the length of the rod produces an e.m.f
in coil L1
 This e.m.f is applied to the base of transistor
 This change of e.m.f. produced an amplified current
change in the circuit
 In the coil L which again cause a change of length of Ni
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68.  In this way oscillation of rod is maintained. The
oscillation frequency f of the Ni rod is controlled by
the variable capacitor C and is given by f = 1/2∏√LC
….. (2)
 If this frequency matches with the natural
frequency of the rod, resonance will occurs
 By adjusting the length of the rod and the capacity
of the condenser, high frequency oscillations of
different frequencies are obtained
 Now the rod vibrates longitudinally with maximum
amplitude and generates ultrasonic wave of high
frequency from its ends
 Frequency can be extended upto 3×105 Hz
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69.  ADVANTAGES
 1. The design of this oscillator is very simple & its
production – low cost
 2. At low US frequencies, the large power output can be
produced without the risk of damage of the oscillatory
circuit
 DISADVANTAGES
 1. It has low upper frequency limit & cannot generate
US frequency above 300 khz
 2.The frequency of oscillations depends on temperature
 3.There will be losses of energy due to eddy current
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70. PIEZO ELECTRIC GENERATOR/
OSCILLATOR
 Based on the phenomenon of “Piezo electric effect”
 Principle- Piezo electric effect
 Transducer  device that converts one form of
energy into another form
 When certain crystals like quartz & tourmaline etc. ,
are stretched or compressed along certain axis (k/a
mechanical axis), an electrical potential difference
is produced along a perpendicular axis (k/a electric
axis)
 The converse of Piezo electric effect is also true 
pressure energy converts into electric energy
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P/B :- DR NIYATI PATEL 70

71. + - + -
- + - +
Mechanical axis
Electrical axis
PRESSURE
APPLICATION
PRESSURE
APPLICATION
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73.  When alternating potential difference is applied
along the electric axis, the crystal is set into
elastic vibration along the corresponding
mechanical axis
 This is k/a “INVERSE PIEZO ELCTRIC EFFECT OR
ELECTROSTRICTION”
 If the frequency of electric oscillations
coincides with the natural frequency of the
crystal, the vibrations will be of large
amplitude
 This phenomenon is utilized for the production
of US waves
 Transducer  device that converts one form of
energy into another form
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74. CONSTRUCTION
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75.  The experimental arrangement is shown in figure
 The high frequency alternating voltage which is applied to
crystal is obtained by Hartley oscillatory circuit
 The Hartley circuit consist of tuned oscillatory circuit
 One end of the tuned circuit is connected to the base of
transistor while the other is connected to the emitter
 The coil L1 & L2 of the oscillator circuit are taken from the
primary of transformer
 Inductor & capacitor are connected parallel
 The crystal plate is sandwiched between metallic foils (AB)
and forms a parallel plate capacitor  This is coupled to
the electronic oscillator through primary coil L3 of the
transformer T
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76. WORKING
 When battery is switched on by pressing switch S
the oscillator produces high frequency
oscillations with frequency f = 1/2∏√L1C1
 The frequency of this oscillations can be varied
with the help of variable capacitor C1
 The e.m.f developed in oscillatory circuit
induces an e.m.f. in coil L3 due to transformer
action
 As a result, the crystal is now under high
frequency alternating voltage
 Inverse Piezo electric effect takes place and the
crystal contracts and expands alternatively. The
crystal is set into mechanical vibrations
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77.  The frequency of the vibration is given by n = P/2l √E/D
 Where P= 1,2,3… etc. for fundamental, first harmonic ,
second harmonic etc
 E = young’s modulus of crystal
 D= density of the crystal
 The capacitor C1 is varied till the frequency of
oscillation matches with the natural frequency of
vibration of the crystal. Under this condition the crystal
generates high power US waves
 The vibrating crystal produces longitudinal US waves of
large amplitude
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P/B :- DR NIYATI PATEL 77

78.  ADVANTAGES
 It is more efficient than magnetostriction oscillator
 US Frequencies as high as 5×108 Hz or 500 MHz can be
obtained with this arrangement
 The output of this oscillator is very high
 It is not affected by temperature & humidity
 DISADVANTAGES
 The cost of Piezo electric quartz is very high
 The cutting & shaping of quartz crystal are very
complex
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79. APPLICATION
 US have found numerous applications in the
following field
1. Communication
2. Industry
3. Scientific world
4. Medical world
They are so useful mainly due to the following
reasons
1. At sufficiently high frequency almost parallel beam
of plan waves can be propagated
2. As the wavelengths are small, measurements can
be made on a small sample without affecting the
physical conditions like temperature, density etc
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80.  1. depth of the sea
 Know that US waves are highly energetic & shows a little
diffraction effect.
 Thus they can be used for finding the depth of the sea
 2. cleaning & clearing
 The waves can be used for cleaning utensils, washing
clothes, removing dust
 3. direction signalling
 US wave can be concentrated into a sharp beam due to
smaller wavelength and hence can be used for signalling
from ship to ship specially in submerged submarines
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81.  4. Metal cutting
 Us wave can be used for drilling and cutting process in
metals
 5. Coagulation & crystallisation
 The particles of a suspended liquid can be brought quite
close to each other using US so that coagulation may
take place which helps in the rate of crystallisation
 6. Disease treatment
 The body part s affected due to neuralgia or rheumatic
pain  US get great relief
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